Planographic printing



Patented June 22, 1954 UNITED STATES PATENT OFFICE PLAN GRAPmC PRINTINGware No Drawing. Application November 28, 1947, Serial No. 788,660

4 Claims.

This invention relates to paper or like cellulose base planographicprinting plates and to a method of and compositions for use in treatingsuch planographic printing plates.

Among the problems involved in the use of paper or like cellulose baseplanographic printing plates are the problems incidental to thererunning of such planographic printing plates upon a planographicprinting press after the initial use or run thereof which includepreventing of image spread during the time the plate is in storage andelimination of excess or residual ink on the printing surface of theplate prior to rerunning. Heretofore in the art it has been customary totreat planographic printing plates, after use, with a preservative, suchas gum arabic, to preserve the image thereon during the time the plateis in storage and to facilitate clean up of the printing surface of theplate prior to rerunning. However, the use of gum arable, as a platepreservativais objectionable in that it must be removed before aplanographic printing plate treated therewith may be reimaged and rerun.Moreover, gum arabic requires considerable care in its application as aplate preservative to avoid danger of blinding the image.

We have now found, however, that if a limited quantity of a finelydivided water-wettable mineral pigment is incorporated in and is looselybound upon the printing surface of a paper or like cellulose baseplanographic printing plate during manufacture thereof, the removal ofinadvertent ink smears from the printing surface of the plate isfacilitated and erasures may be more easily efiected, and the thusprepared plate may be readily cleaned and conditioned for rerunning bythe application of a water dispersion of such finely divided mineralpigment to the printing surface of the plate, after use and prior tostor age, without the necessity for removal of the plate preservativecomposition thus applied as is necessary in the use of gum arabic orsimilar plate preservative compositions.

More specifically, we have found that if the new platepreservativecomposition, in the form of a water dispersion of a finely dividedwater- ,wettable mineral pigment, is applied to the printing surface ofa coated paper or like cellulose base planographic printing plate havinga limited quantity of such finely divided water-wettable loosely boundmineral pigment incorporated therein in the manufacture thereof, afteruse, and. before rerunning, image spread during storage is effectivelyprevented and residual ink on the printing surface of the plate isquickly and nil-14.9.2)

effectively removed. Thus the plate may be removed from storage andrerun without the necessity for the removal of the plate preservativecomposition and with the result that in the rerunning of the platesatisfactory numbers of excellent copies are obtained which are substantially free of ink specks and generally as good in quality as the copiesobtained in the first edition or run of the plate.

Accordingly, an object of the present invention is to provide a new andimproved coated paper or like cellulose base planographic printing platehaving incorporated in the printing surface thereof a limited quantityof a finely divided Water-wettable loosely bound mineral pigment whichnot only affords an excellent planographic printing surface but promotesand facilitates quick and easy clean up of the plate and prevention ofimage spread during the time the plate is in storage.

Another object of the invention is to provide a new and improved methodof and clean-up and plate preservative compositions for use in eifectingquick and easy clean-up of the printing surface of a planographicprinting plate, of the character contemplated by the present invention,after use, and prevention of image spread While the thus treated plateis in storage, without the necessity for removing the plate preservativecomposition from the printing surface of the plate after storage inorder to add further images to the plate prior to rerunning it, as isnecessary in the use of gum arabic and like plate preservativecompositions.

A further object of the present invention is to provide a new andhnproved method of and clean-up and plate preservative compositions foruse in efiecting quick and easy clean up of the new planographicprinting plates after running and before storage and to the end that theplates may be removed from storage and immediately applied to and rerunupon a rotary offset pianographic printing press with the result thatcopies are obtained which are substantially free of ink specks and areotherwise as good in quality as the copies obtained in the first run oredition of the plate.

Other objects will appear hereinafter.

In the practice of the present invention the finely divided,water-wettable mineral pigment may be applied to and incorporated in theprinting surface of the new coated planographic printing plate as aloosely bound pigment as distinguished from the usual practice oftightly binding pigments in or upon the coated surfaces of paper sheetsby means of a suitable adhesive hinder or the like. When the thus finelydivided water-wettable loosely bound mineral pigment is incorporated inthe printing surface of the plate it provides a pattern of capillaryspaces which are water-receptive and ink-receptive but are be lieved toprevent image spread by preventing lateral difiusion of the oilcomponent of the printing ink applied thereto. At the same time, theabrasive surface of the thus formed plate permits of ready ink removaland thus makes possible quick and easy clean up of the plate after use.

Typical procedures which may be followed in the practice of the presentinvention will now be described.

Example No. 1

A coated paper base planographic printing plate was provided with atypewritten image and with a crayon image and three hundred (300) copieswere run therefrom upon a rotary offset planographic printing press. Theplate was then removed from the press and while still wet, was wipedlightly with a cotton swab saturated with a clean-up and platepreservative composition in the form of a water dispersion of a finelydivided water-wettable mineral pigment consisting of a one (1) per centsilica aquasol prepared according to the process disclosed in UnitedStates Patent No. 2,375,738 granted May 8, 1945, to John Example No. 2

The procedure set forth in'the foregoing Example No. l was followedexcept that the cleanup and plate preservative composition was in theform of a two (2) per cent silica aquasol or aqueous suspension ofcolloidal silica in place of the one (1) per cent solution as employedin Example In place of the silica aquasol specified in the foregoingExamples Nos. 1 and Z'other forms of finely divided silica may be usedand these materials may be employed in water dispersions thereof inwhich the silica component is maintained within the limits of from about0.2 per cent to about 5.0 per cent,'by weight, of the complete clean-upand plate preservative composition with an optimum of about one (1) percent.

' Likewise, place of the silica aquasol specified in the foregoingExamples Nos. 1 and 2, water dispersions of any of the 'finely dividedwaterwettable mineral pigments specified in the followmg examples may beemployed-as the new cleanup and plate preservative composition:

Example N o. 3

Hydrated aluminum oxide "grams" Water c.'c 495 Example No. 4

Kaolin (china clay) r grams 5 Water -ic. c. 495

4 7 Example No. 5 Bentonite grams 5 Water c.c 495 Example No. 6

Zinc Oxide grams 5 Water c.c 495 sample No. 7

Talc "grams" 5 Water c.c 495 Example No. 8 Diatomaceous earth (finelydivided) grams a Water c,c 396 Example No. 9

Calcium carbonate (finely divided) grams 4 Water c.c' 396 Example No,10'

Barium sulphate (iine ly divided) grarns a Water l c.ci 396 Themateriais referred to in the foregoing Examples Nos, 3 to 10, inclusive,may be prepared .for use as clean-up and plate preservative compositionsby dispersing the solid component, in finely divided form, in the liquidcomponent (water) by vigorous agitation, redispersion being effected byshaking the plate preservative composition after standing and beforeapplication to the printing surface of a paper or like cellulose baseplanographic printing plate. In some instances, as in the case ofbentonite, redispersion may be more difficult than in other cases andmay require more prolonged shaking before application. 7

All of the solid components of the compositions referred to in theforegoing Examples Nos. 1 to 10, inclusive, are characterized b beingfinely divided water-wettable mineral pigments which are insoluble inwater while being otherwise. suit able for their intended uses, asdescribed.

In the practice of the present invention, in one phase thereof, thefinely divided water-wettable mineral pigment may be incorporated in andloosely bound upon the wash-coat or a coated paper or like cellulosebase planographic printing plate, as illustrated in the followingexamples i Example No. 11

A paper sheet having wet strength properties and weighing about 25pounds per thousand square feet was coated on each side with 6 pounds drweight per thousand square feet of a coating containing clay 100 partsand casein 20 parts.

The coated sheet was calendered and then given a wash-coat, on one side,of about 0.5 lb.'dry weight per thousand square feet of an aqueoussolution containing 1 percent or sodium alginate and 0.6 per cent ofammonium bichromate. The

sheet was then washed with a 2 per cent aqueous dispersion of a sliceaquasol. The silica thus applied was loosely bound upon the surface or"the sheet which, when dried and used. as a pianographic plate, was veryclean after 300 satisfactory impressions had been'made therefrom.

The printing surfaces prepared according to Example l or Example 2 abovemay be further improved as follows:

Example No. 12 The dried surfaces of the paper product to which adispersion of silica aquasol had been applied, as describedin ExampleNo; 11, were treated with a wash coat in the form of an aqueous solutionof a water-soluble and waterstable divalent metal salt, after the mannerdescribed for treating planographic printing surfaces in the copendingapplication of the applicant, Stephen V. Worthen, Serial No. 170,486filed June 26, 1950, now Patent No. 2,534,650.

Example No. 13

To an aqueous dispersion containing 1.5 per cent of silica, in the formof a hydrosol, was added a 10 per cent aqueous dispersion of caseinwhich had been solvated by ammonia, said addition being sufiicient tointroduce one part of casein for each 3 parts of S102 present. Theresulting suspension was then applied to a calendered paper productconsisting of a wet-strength paper base Weighing 30 pounds per 1000square feet and bearing a coating of 6 pounds per 1000 square feetcontaining 5 parts of clay to 1 part of casein adhesive. When so appliedthe finely divided silica was loosely bound upon the printing surface ofthe sheet which was wet-out very readily and, when used as aplanographic printing plate, gave over 500 satisfactorily cleanimpressions.

All of the finely divided water-wettable mineral pigments referred to inthe clean-up and plate preservative compositions set forth in ExamplesNos. 3 to 10, inclusive, may be incorporated in and loosely bound uponthe printing surface of the new planographic printing plates in themanner described in the foregoing Examples Nos. 11, 12 and 13. When soused these materials are preferably employed in a quantity of from about0.2 to 5.0 per cent, by weight, of the aqueous dispersion in which suchmaterial may be applied to and incorporated in the printing surface ofthe plate.

When bentonite is employed as the finely di vided water-wettable mineralpigment, in the practice of the present invention, it is preferablyemployed only when preparing a colorless planographic printing platesince it may interfere with the organic or other coloring materialsemployed in preparing a colored planographic printing plate.

Example N0. 14

The procedure set forth in Example No. 1 was followed except that a newimage was applied to a previously unimaged area and, likewise, a portionof the original image on the plate was removed by erasure and a newimage typed on the erased area after storage and before rerunning. Theimages afforded by the newly imaged area and likewise by the erased andreimaged area were as good in quality as those obtained from theoriginal and non-erased areas.

All of the finely divided water-wettable mineral pigments used in thepractice of the present invention have the necessary tooth required forthe reception of a planographic image and also for the reception of theaqueous planographic etching and dampening solutions which are employedin planographic printing upon rotary 011- set planographic printingpresses and the like.

In the preparation of the clean-up and plate preservative compositionsspecified in each of the foregoing Examples Nos. 3 to 10, inclusive, thesolid component of the water dispersion is preferably maintained at aconcentration of about one 151) per cent by weight, of the totalcomposiion.

It will thus be seen from the foregoing description that the presentinvention affords a novel method of and compositions for treating apaper or like cellulose base planographic printing plate, and has thedesirable advantages and characteristics, and accomplishes its intendedobjects, including those hereinbefore specified, and others which areinherent in the invention.

We claim:

1. In the art of preparing direct image planographic printing plates,the improvement which consists in providing a paper or like cellulosicbase sheet with a planographic base coating having therein finelydivided pigment particles, applying directly upon the external surfaceonly of said planographic base coating an auxiliary coating consistingof a water dispersion of a finely divided hydrophilic water insolublenon-reactive mineral pigment in the form of a silica aquasol, and thenbonding the pigment particles of the said water dispersion to the saidbase coating by drying to form a discontinuous deposit of discreteparticles of said finely divided mineral pigment over the entireexternal surface only of said planographic base coating.

2. A planographic printing plate which is the product of the methoddefined in claim 1.

3. In the art of printing from a direct image coated planographic paperor like cellulosic base planographic printing plate provided with ahydrophilic planographic image-receptive surface having thereon greasyhydrophobic images defining printing portions, the improvement whichresides in printing from the said imagebearing planographic printingplate, applying to the said printing surface of said direct imageplanographic printing plate, after printing therefrom, a clean-up andplate preservative composition composed of a water dispersion of afinely divided water-insoluble non-reactive water-wettable hydrophilicmineral pigment whereby to cover only the unimaged areas thereof, dryingthe thus treated planographic printing plate, and then reprinting fromthe said treated and dried planographic printing plate without removingthe said clean-up and plate preservative composition from the unimagedareas thereof prior to the said reprinting operation.

4. The improvement in the art of printing from a direct image paper orlike cellulosic base planographic printing plate, as defined in claim 3,in which the said clean-up and plate preservative composition is in theformE of a silica aquasol.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 606,709 Five July 5, 1898 637,588 Hett Nov, 21, 1899 2,132,443Simons Oct. 11, 1938 2,154,219 Shepherd Apr. 11, 1939 2,156,100 SimonsApr. 25, 1939 2,233,573 Ayers Mar. 4,1941 2,280,986 Toland Apr. 28, 19422,361,665 Toland Oct. 31, 1944 FOREIGN PATENTS Number Country Date 4,930Great Britain Nov. 10, 1881

